CO, Lambda and O2 sensor question?

[Fast Guy]

Probably one for Ed this unless someone else knows for sure.

On the MOT test (I'm sure he did the wrong one) I thought lambda and CO were related? Lambda I thought was the mixture relative to the stochiometric ratio of 14.7:1 and I thougt CO was the old way of measuring the same before the started measuring Lambda on cat vehicles. So if they're not, what are they?

My CO was 0.15 and my Lambda was 1.19 (I think) It was passing on the CO (against a limit of 0.2:der but failing on the lambda against it's limit (1.1ish I think)
That was at a fast idle speed.

At normal idle it was showing around 5%:shock: The first year with the mongoose it was well under 0.1% CO

So, does the O2 sensor just sort out idle fuelling, ie my lambda sensor is probably shot? Or does it do the fuelling elsewhere?

Anyway I convinced him he was doing the wrong test as it was showing Dec 92 on the machine and my car's a J reg which means it can't be a Dec, so should be <3.5% for a july 92 non cat test.

I'm fairly sure my engine coolant sensor is working as the test was going on for so long the fans came on.:doh:

 

[ChrisS]

The O2 sensor keeps the mixture to 14.7:1 but being a narrow band it only knows if the mixture is richer or leaner than that and then adjusts up and down accordingly. It does this whilst in closed loop mode, so basically idle/low load areas of the fuel map. Once it goes into the higher load areas (open loop) the ecu then works against the preset values within the map.

Ive not seen lambda inclused in the emmissions test for MOT, only CO and HC.

My car idles at 14/7:1 to 15:1 and the CO result on last years test was 2.343. HC levels were a little close to the limit at 1138

 

[pulsarboby]

as chris said above!
the lambda is overiden by the ecu on anything other than above fast idle and closed loop.

if you have a dodgy one you can find that your hc level will at idle test rise as this is basically unburnt fuel not being metered by the ecu correctly, but this can also be caused by many other things also such as poor ignition with weak spark, blocked or restricted air filter other dodgy sensors.

i also thought that co emission limit was 0.5 unless this has been dropped recently that is, thats with cat but without on earlier cars the limit is 3.5.
so in a nutshell if the hydrocarbons are high on your car then i would first take a look at your ignition system and possibly leaky injectors

 

[Fast Guy]

It's the first time I've seen Lambda measured on the test too, which initially made me think he's doing the wrong test for my car.

So the chances are high idle CO is the lambda sensor?
I think I might change the Lambda sensor for the sake of it. (I still have the cat available if all else fails, mind you, 5-6years in my outside shed could have killed it by now.)

I think my HCs were a little high but in limit at idle speed, but everything was pretty good at fast idle.

CO limit is less than 3.5% on J reg (July 92) or earlier cars.

I did think about the filter and maybe giving it a blow out with compressed air. It's an Apexi induction kit.

 

[pulsarboby]

So the chances are high idle CO is the lambda sensor?

yes, you can measure the voltage output of lambda to show if its working correctly but cant remember what the reading should be without looking it up.

little tip for you though before replacing it.....take it out and clean the probe with some carb cleaner, they often get sooted up on short journeys and this will affect the readout, also give the car a good thrashing before its retested to make sure its nice and hot that makes a difference too.
i reckon if you do that itll go through ok

 

[Fast Guy]

I gave it a good thrash before the test, but it didn't work. I just change it before the next test. Chances are it's still the origional one, so it won't hurt to change it.

 

[campbellju]

Carl, if your lambda is truly 1.19 that equates to 17.5 AFR. Link this to high HC's and it means you are getting lean mifires. The high HC's are becuase the fuel is coming out unburnt. The Lambda is lean because the mixture isn't igniting rather than you getting some super clean burn. By not burning the mixture your CO stays low. I had similar problems that I solved with a little mapping and some new plugs with wider plug gaps.


It could be lambda sensor and it could be excess air (air leak) but don't rule out your ignition system either.

Jim

 

[Fast Guy]

I take it 17.5 is lean then? Why does the machine fail it for being lean?

 

[campbellju]

If you have a very lean mixture then you get NOx issues.

 

[skiddusmarkus]

Has anyone used one of these?

http://www.amazon.co.uk/Oxygen-Sensor-Nissan-UNIVERSAL-1-4-wire/dp/B004U0SJFO

Got to be better than paying £100+.Mine is reading 2.5v so is in what's known as spazzmode.

 

[j0ff]

if they're the same fitting as the skyline, you can get a generic one on ebay for £20 (so long as you're happy to solder). There was a lot of talk on the skyline owners forum and a huge number had changed them for a generic one and all reckoned they were fine. I'll find the link for the one I bought last year.

 

[j0ff]

http://www.ebay.co.uk/itm/ws/eBayIS...PageName=ADME:B:EOIBSA:GB:1123#ht_4025wt_1161
this is the one I fitted. Not sure what the general opinion on here is for fitting generic lambda sensors. Don't flame me...

 

[Drift God]

Just had my R for mot and only failed on emissions. was 6.5% Co. bought a gunson gas tester (only 80quid halfords) i sorted it by just adjusting the fuel regulator and got it to 0.6% with no Cat. retest on sat. mine is 1994 L reg but yet still falls in the 3.5% bracket???????

Yea just like mentioned before lambda 1 = stochiometric (supposed perfect burn) above lambda 1 = lean mixture and below lambda 1 = rich micture. 0.85 lambda is the sweet spot for the maximum power output for motorsport applications, but obviously leads to higher hc (unburnt fuel)

 

[Drift God]

Also was thinking, have you a split in any of your hoses after the AFM? in that case the engine is getting more air than the ecu is getting registered from the AFM which would lead to a leaner mixture and reading. just a thought been known to happen.

 

[Fast Guy]

Do you have a wideband gauge Simon as you can switch it O2 off in Nistune.
Another thing I noticed, on my knock fuel map, it was set to 12s in the idle region which would tie in with high idle emissions, so I pulled mine back in to 14.7, now it seems OK.

 

[skiddusmarkus]

http://www.ebay.co.uk/itm/ws/eBayIS...PageName=ADME:B:EOIBSA:GB:1123#ht_4025wt_1161
this is the one I fitted. Not sure what the general opinion on here is for fitting generic lambda sensors. Don't flame me...

So the M18 fitted fine then?

 

[j0ff]

So the M18 fitted fine then?

That was for the skyline, haven't a clue about gtir, I was just pointing out that generic O2 sensors work fine on the skyline, I'd assume they'd also be fine on the gtir

 

[danr]

That was for the skyline, haven't a clue about gtir, I was just pointing out that generic O2 sensors work fine on the skyline, I'd assume they'd also be fine on the gtir

Nop, GTiR is titanium sensor, has red wire. ~£40.